The present invention relates generally to a transparent flexible barrier and, more particularly, to a transparent flexible barrier for liquid crystal display devices and methods of making the same.
Active-matrix liquid-crystal displays (LCDs) are widely used as displays for different applications and are the standard on high-end laptop computers. In a liquid crystal display the liquid crystal is held between two glass plates. These plates are usually manufactured with transparent electrodes, typically made of indium tin oxide (ITO) that make it possible to apply an electric field across small areas of the liquid crystal film. The outer surfaces of these plates are coated with filters to polarize the light entering and leaving the crystal. Usually these filters are crossed, which means that, normally, no light would be able to pass through the display. The liquid crystal, however, will modify the polarization of the light in some way that is dependent on the electric field being applied to it. Therefore, it is possible to dynamically create regions where light passes through and other regions where it does not.
The attractive design opportunities offered by flat and flexible displays as well as their low-cost manufacturing potential have led to significant interest in plastic-based liquid crystal displays.
However, many liquid crystal materials undergo detrimental reactions with oxygen and moisture. To function over extended periods of time the LCD devices must be sealed to prevent contact of the liquid crystal material with water and oxygen. Whereas this does not pose a problem when impermeable glass plates are used, it is a major concern in the case of flexible LCD displays that employ flexible polymeric substrates.
In order to have a LCD display with a lifetime of 10 years or greater, the water vapor and oxygen permeation rate through the polymeric substrate used should be about xe2x89xa61 g/m2-day and about xe2x89xa60.1 cm3/m2-day, respectively. None of the currently available polymeric substrates are able to meet the stringent permeability barrier requirements that are necessary for use as a substrate for LCD devices. In order to provide these properties, the polymeric substrate must therefore receive some type of treatment to sufficiently reduce the permeability of the LCD to both water and oxygen.
Accordingly, there is a need in the art for an improved polymeric-based transparent flexible material for use with liquid crystal display devices.
This invention meets this and other needs by providing a flexible liquid crystal display that includes a water and oxygen permeability barrier that is deposited on a polymeric substrate, a barrier coated polymeric sheet for use in such liquid crystal displays, a method of making such a barrier coated polymeric sheet, and an apparatus for coating a continuous sheet of polymeric substrate with a barrier layer.
Accordingly, one aspect of the present invention is to provide a flexible liquid crystal display. The flexible liquid crystal display comprises two plates that are substantially parallel to each other, wherein each of the plates comprises: a polymeric substrate having a surface roughness of up to about 5 nm; a barrier coating disposed on a surface of the polymeric substrate; and a transparent conductive layer disposed on a surface of the barrier coating opposite the polymeric substrate. The flexible liquid crystal display also comprises a liquid crystal material disposed between the two plates, such that the liquid crystal material contacts the transparent conductive layer on each of the two plates.
A second aspect of the invention is to provide a barrier coated polymer sheet for use in a liquid crystal display. The barrier coated polymer sheet comprises a polycarbonate substrate having a surface roughness of up to about 5 nm; and a barrier coating disposed on a surface of the polycarbonate substrate, wherein the barrier coating has a density of at least 1.8 g/cm3.
A third aspect of the invention is to provide a flexible liquid crystal display. The flexible liquid crystal display comprises two plates that are substantially parallel to each other, wherein each of the plates comprises: a polycarbonate substrate having a surface roughness of up to about 5 nm; a barrier coating disposed on a surface of the polycarbonate substrate; and a transparent conductive layer disposed on a surface of the barrier coating opposite the polycarbonate substrate. The flexible liquid crystal display also comprises a liquid crystal material disposed between the two plates, such that the liquid crystal material contacts the transparent conductive layer on each of the two plates. Each of the plates has an oxygen permeation rate of no greater than about 0.1 cm3/m2-day and a water vapor transmission rate of no greater than about 1.0 g/m 2-day.
A fourth aspect of the invention is to provide a method of making a barrier coated polymer sheet for use in a liquid crystal display. The barrier coated polymer sheet comprises a polycarbonate substrate having a surface roughness of up to about 5 nm and a barrier coating disposed on a surface of the polycarbonate substrate, wherein the barrier coating has a density of at least 1.8 g/cm3. The method comprises the steps of: providing the polycarbonate substrate; and depositing the barrier coating on the surface of the polycarbonate substrate by plasma enhanced chemical vapor deposition.
Finally, a fifth aspect of the invention is to provide an apparatus for coating a continuous sheet of polymeric substrate with a barrier layer. The apparatus comprises: a rotatable drum contacting a first surface of the sheet, wherein the rotatable drum and sheet are heatable to a predetermined temperature; a substrate supply for supplying a continuous feed of the sheet to the rotatable drum; at least one deposition device for depositing the barrier layer, the barrier layer comprising at least one of silicon nitride, silicon oxide, aluminum oxide, and combinations thereof on a second surface of the sheet; a sheet collection device for collecting the sheet after the sheet has contacted the rotatable drum and the barrier layer has been deposited on the sheet; and a vacuum chamber for maintaining the rotatable drum, substrate supply, deposition device, and sheet collection device at a predetermined pressure, the vacuum chamber enclosing the rotatable drum, substrate supply, deposition device, and sheet collection device, wherein the vacuum chamber is in communication with a pumping system.
These and other aspects, advantages, and salient features of the present invention will become apparent from the following detailed description, the accompanying drawings, and the appended claims.